Each year millions of people resolve to get fit, but they quit when their gym sessions don't reap immediate results. According to Brian Sharkey, a leading fitness researcher and educator, people often fall prey to common fitness misconceptions that prevent them from achieving their goals. In his upcoming book, Fitness Illustrated (Human Kinetics, October 2010), Sharkey dispels the top fitness fallacies.

No pain, no gain. Pain is not a natural consequence of exercise or training. Rather, it signals a problem that you need to address. Discomfort, however, can accompany difficult training such as heavy lifting, intense interval training and long-distance work. The discomfort results naturally from the lactic acid that accompanies the anaerobic effort of lifting or doing intense intervals. "Overload is necessary for adaptation, and it sometimes requires working at the limit of strength, intensity, or endurance, which can be uncomfortable," Sharkey says. "But, if your exercise results in outright pain, it's probably excessive."

You must break down muscle in order to improve. Neither pain nor injury is a normal result of training. Runners often experience microtrauma at the end of a marathon that includes downhill stretches requiring eccentric muscular contractions. "Such contractions are a major cause of muscle soreness, which is associated with muscle trauma, reduced force output, and a protracted recovery period (four to six weeks)," Sharkey says. "Thus 'breaking down' muscle does not help training, but instead brings it to a standstill."

Go for the burn. This mantra is often heard among bodybuilders who do numerous repetitions and sets to build, shape, and define their muscles. "They are probably referring to the sensation felt when the level of lactic acid increases in a muscle," Sharkey explains. "This sensation is not dangerous, but it isn't necessary."

Lactic acid causes muscle soreness. Lactic acid may be produced when performing contractions that lead to soreness, but lactic acid does not cause the soreness. Lactic acid clears from the muscles and blood within an hour after exercise. "Muscle soreness is probably related to microtrauma in muscle and connective tissue, and resultant swelling, caused by engaging in a new kind of exertion or exercise after a long layoff," Sharkey says.

Muscle turns to fat. Many people believe that if they stop training, their muscle will turn to fat. Neither muscle nor fat will turn into the other. "Muscle grows or gets smaller because training increases the size of muscle fibers (hypertrophy), whereas detraining reduces the size of these fibers (atrophy)," Sharkey explains. "Fat cells, in contrast, grow in size as they store more fat as the result of excess caloric consumption. If, on the other hand, you use more calories than you take in, fat cells shrink."

I ran out of wind. When a person runs too fast for his level of training, he may feel as if he has run out of wind. This is due not to a lack of oxygen but instead to an excess of carbon dioxide, which is produced when the body metabolizes carbohydrate. "The respiratory system decides that it is more important to rid the body of excess CO2 than to bring in more O2," Sharkey says. "Excess CO2 is a signal that the body is working above its level of training -- and it has exceeded the level of exertion it can sustain."

If seen on TV, it must be true. The 30-minute sales pitches on television for fitness equipment or exercise systems promise quick results, but these claims are never backed by evidence -- just unverified testimonials. "That equipment will soon clutter the garage, basement, or attic, and there will be a new exercise miracle on TV in a few months," Sharkey says. "If it sounds too good to be true, it probably is."

Brian Sharkey, PhD, is a leading fitness researcher, educator, and author. Sharkey has more than 45 years of experience in exercise, sport, and work physiology. He is professor emeritus at the University of Montana, where he served as director of the Human Performance Laboratory and remains associated with the university and lab. He currently serves as a consultant with several federal agencies in the areas of fitness, health, and work capacity, especially of wildland firefighters. He has won several awards for his work, including the 2009 International Association of Wildland Fire's Wildland Fire Safety Award for his contributions to wildland firefighter safety and health.

Sharkey authored or contributed to over a dozen books on exercise, sport, and work physiology and fitness and numerous research papers. He is past president of the American College of Sports Medicine and served on the NCAA committee on competitive safeguards and medical aspects of sports, where he chaired the Sports Science and Safety subcommittee, which uses research to improve the safety of intercollegiate athletics. He also coordinated the United States ski team Nordic Sports Medicine Council.